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          LV05-01-uboot-09-uboot中的SPL
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<details class="folding-tag" blue><summary> 点击查看使用工具及版本 </summary>
              <div class='content'>
              <table>    <tr>        <td align="center" width=150px>Windows版本</td>        <td align="left">windows11</td>    </tr>    <tr>        <td align="center">Ubuntu版本</td>        <td align="left">Ubuntu16.04的64位版本</td>      </tr>    <tr>        <td align="center">VMware® Workstation 16 Pro</td>        <td align="left">16.2.3 build-19376536</td>      </tr>    <tr>        <td align="center">终端软件</td>        <td align="left">MobaXterm(Professional Edition v23.0 Build 5042 (license))</td>      </tr>    <tr>        <td align="center">Linux开发板</td>        <td align="left">正点原子 i.MX6ULL Linux 阿尔法开发板</td>      </tr>    <tr>        <td align="center">uboot</td>        <td align="left">NXP官方提供的uboot，NXP提供的版本为uboot-imx-rel_imx_4.1.15_2.1.0_ga(使用的uboot版本为U-Boot 2016.03)</td>      </tr>    <tr>        <td align="center">linux内核</td>        <td align="left">linux-4.15(NXP官方提供)</td>      </tr>    <tr>        <td align="center">Win32DiskImager</td>        <td align="left">Win32DiskImager v1.0</td>      </tr></table>
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            </details>

<details class="folding-tag" blue><summary> 点击查看本文参考资料 </summary>
              <div class='content'>
              <table>    <tr>        <td align="center">分类</td>        <td align="center">网址</td>        <td align="center">说明</td>    </tr>    <tr>        <td align="center" rowspan="5">官方网站</td>        <td align="left"><a href="https://www.arm.com/" target="_blank">https://www.arm.com/</a></td>        <td align="left">ARM官方网站，在这里我们可以找到Cotex-Mx以及ARMVx的一些文档</td>    </tr>    <tr>        <td align="left"><a href="https://www.nxp.com.cn/" target="_blank">https://www.nxp.com.cn/ </a></td>        <td align="left">NXP官方网站</td>    </tr>    <tr>        <td align="left"><a href="https://www.nxpic.org.cn/" target="_blank">https://www.nxpic.org.cn/</a></td><td align="left">NXP 官方社区</td>    </tr>    <tr>        <td align="left"><a href="https://u-boot.readthedocs.io/en/latest/" target="_blank">https://u-boot.readthedocs.io/en/latest/</a></td><td align="left">u-boot官网</td>    </tr>    <tr>        <td align="left"><a href="https://www.kernel.org/" target="_blank">https://www.kernel.org/</a></td><td align="left">linux内核官网</td>    </tr></table>
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<details class="folding-tag" blue><summary> 点击查看相关文件下载 </summary>
              <div class='content'>
              <table>    <tr>        <td align="center">分类</td>        <td align="center">网址</td>        <td align="center">说明</td>    </tr>    <tr>        <td align="center" rowspan="4">NXP</td>        <td align="left"><a href="https://github.com/nxp-imx" target="_blank">https://github.com/nxp-imx</a></td>        <td align="left">NXP imx开发资源GitHub组织，里边会有u-boot和linux内核的仓库</td>    </tr>    <tr>        <td align="left"><a href="https://elixir.bootlin.com/linux/latest/source" target="_blank">https://elixir.bootlin.com/linux/latest/source</a></td>        <td align="left">在线阅读linux kernel源码</td>    </tr>    <tr>        <td align="left"><a href="https://github.com/nxp-imx/linux-imx/releases/tag/rel_imx_4.1.15_2.1.0_ga" target="_blank">nxp-imx/linux-imx/releases/tag/rel_imx_4.1.15_2.1.0_ga</a></td>        <td align="left">NXP linux内核仓库tags中的rel_imx_4.1.15_2.1.0_ga</td>    </tr>    <tr>        <td align="left"><a href="https://github.com/nxp-imx/uboot-imx/releases/tag/rel_imx_4.1.15_2.1.0_ga" target="_blank">nxp-imx/uboot-imx/releases/tag/rel_imx_4.1.15_2.1.0_ga</a></td>        <td align="left">NXP u-boot仓库tags中的rel_imx_4.1.15_2.1.0_ga</td>    </tr>    <tr>        <td align="center" rowspan="2">I.MX6ULL</td>        <td align="left"><a href="https://www.nxp.com.cn/docs/en/data-sheet/IMX6ULLIEC.pdf" target="_blank">i.MX 6ULL Applications Processors for Industrial Products</a></td>        <td align="left">I.MX6ULL 芯片手册（datasheet，可以在线查看）</td>    </tr>    <tr>        <td align="left"><a href="https://www.nxp.com.cn/webapp/Download?colCode=IMX6ULLRM&lang_cd=zh" target="_blank">i.MX 6ULL Applications ProcessorReference Manual</a></td>        <td align="left">I.MX6ULL 参考手册（下载后才能查看，需要登录NXP官网）</td>    </tr></table>
              </div>
            </details>

<p>u-boot里面，有一个叫做 SPL 的东东，我们在看 u-boot 代码的时候，很多地方都可以看到和它相关的东西，这里了解这玩意到底是拿来干啥用的。</p>
<h1 id="一、SPL名字怎么来的？"><a href="#一、SPL名字怎么来的？" class="headerlink" title="一、SPL名字怎么来的？"></a><font size=3>一、SPL名字怎么来的？</font></h1><p>SPL 全称叫做：<strong>Secondary Program Loader</strong>，看名字，像是一个什么二级加载相关的；实质上，也就是是二级加载。</p>
<p>我们知道u-boot 是用来引导启动我们的嵌入式系统的，那为什么不直接使用 u-boot ？为何还会多出一个 u-boot spl 呢？那我们从系统启动开始说起吧。</p>
<p>站在芯片厂商的角度来说，硬件系统一上电，一定是要去某个地址取指令（一般是 0x00000000），然后软件便开始很欢快的运行起来了；通常来讲，SoC 厂家都会做一个 ROM 在 SoC 内部，这个 ROM 很小(主要还是因为成本)，里面固化了上电启动的代码（<strong>一经固化，永不能改</strong>，是芯片生产的时候，做进去的）；这部分代码呢，我们管它叫做 BootROM（或者随便叫也行）。</p>
<p>换句话来说，上电后，先接管系统的是 SoC 厂家的 BootROM，它要做些什么事情呢？初始化系统，CPU 的配置，关闭看门狗，初始化时钟，初始化一些外设（比如 USB Controller、MMC Controller，Nand Controller 等）；我们管这个 BootROM 叫做一级启动程序，而排在后面的就叫二级启动，这就是 SPL 名字的由来。</p>
<h1 id="二、为什么要有SPL？"><a href="#二、为什么要有SPL？" class="headerlink" title="二、为什么要有SPL？"></a><font size=3>二、为什么要有SPL？</font></h1><h2 id="1-需要先知道的事？"><a href="#1-需要先知道的事？" class="headerlink" title="1. 需要先知道的事？"></a><font size=3>1. 需要先知道的事？</font></h2><p>如果是大芯片（不是单片机），外挂了存储设备（eMMC、Nand、SDCard 等）和内存 RAM（SDRAM、DDR 等），通常情况下呢，我们要让系统跑起来，需要先烧写代码，这个烧写代码，其实是将可执行的二进制文件写到外部的存储设备上（eMMC、Nand、SD Card 等）；系统上电启动的时候呢，去把他们读到内存中去执行。</p>
<p>前面我们说了，上电后，其实SoC 厂家自己的 BootROM，其他可执行的程序（u-boot、Kernel）都放（烧写）到了外部存储器。那么BootROM 的代码除了去初始化硬件环境以外，还需要去外部存储器上面，将接下来可执行的程序读到内存来执行。</p>
<p>既然是读到内存执行，那么这个内存可以不可以是我们板载的 DDR 呢？理论上是可以的，但是，SoC 厂家设计的 DDR 控制器呢，一般会支持很多种类型的 DDR 设备，并且会提供兼容性列表，SoC 厂家怎么可能知道用户 PCB 上到底用了哪种内存呢？所以，直接把外部可执行程序读到 DDR 显然是不太友好的，一般来说呢，SoC 都会做一个内部的小容量的 SRAM （又是成本），BootROM 将外部的可执行程序从存储器中读出来，放到 SRAM 去执行。</p>
<p>好了，现在我们引出了 BootROM和内部SRAM；那么 BootROM 从具体哪个存储器读出二进制文件呢？SoC 厂家一般会支持多种启动方式，比如从 eMMC 读取，从 SDCard 读取，从 Nand Flash 读取等等；上电的时候，需要告诉它，它需要从什么样的外设来读取后面的启动二进制文件。</p>
<p>一般的设计思路是，做一组 Bootstrap Pin，上电的时候呢？BootROM 去采集这几个 IO 的电平，来确认要从什么样的外部存储器来加载后续的可执行文件。比如呢，2 个 IO，<code>2&#39;b00</code> 表示从 Nand 启动，<code>2&#39;b01</code> 表示从 eMMC 启动，<code>2&#39;b10</code> 表示从 SDCard 启动等等。</p>
<p>BootROM 读到这些值后，就会去初始化对应的外设，然后来读取后面要执行的代码；这些 IO 一般来说，会做成板载的拨码开关，用于调整芯片的启动方式。</p>
<p>这里，多说一句，读取烧写的二进制的时候呢，需要注意一些细节，比如，SoC 厂家告诉我们，我们需要先把 SDCard 初始化称为某种文件系统，然后把东西放进去才有效之类的；因为文件系统是组织文件的方式，并不是裸分区；我们按照 A 文件系统的方式放进去，然后 SoC 的 BootROM 也按照 A 文件系统的方式读出来，才能够达成一致。</p>
<h2 id="2-进入正题——SPL？"><a href="#2-进入正题——SPL？" class="headerlink" title="2. 进入正题——SPL？"></a><font size=3>2. 进入正题——SPL？</font></h2><p>前面说了，BootROM 会根据 Bootstrap Pin 去确定从某个存储器来读可执行的二进制文件到 SRAM 并执行；理论上来说，这个二进制文件就可以是我们的 u-boot.bin 文件了；也就是 BootROM 直接加载 u-boot.bin。</p>
<p>理论上是这样的，但是这里有一个问题，就是 SRAM 很贵，一般来说，SoC 的片上 SRAM 都不会太大，一般 4KB、8KB、16KB…256KB不等；但是呢，u-boot 编译出来，却很大，好几百KB，放不下的。放不下怎么办？有两种办法：</p>
<blockquote>
<p>1、放不下就放不下呗，BootROM 加载多少算多少；</p>
<p>2、做一个小一点的 boot 程序，先让 BootROM 加载这个小的程序，后面再由这个小 boot 去加载 u-boot；</p>
</blockquote>
<p>比如，我们的 u-boot 有 300KB，SRAM 有 8KB，外部 DDR 1GB：</p>
<ul>
<li>如果使用第一种方案的话，u-boot 的前面 8K 被加载进入 SRAM 执行，u-boot 被截断，我们就需要保证在 u-boot 的前 8KB 代码，把板载的 DDR 初始化好，把整个 u-boot 拷贝到 DDR，然后跳转到 DDR 执行；</li>
<li>第二种方案的话，我们做一个小的 u-boot ，这个 u-boot 就叫做 spl，它很小很小（小于SRAM大小），它先被 BootROM 加载到 SRAM 运行，那么这个 spl 要做什么事情呢？最主要的就是要初始化 DDR Controller，然后将真正的大 u-boot 从外部存储器读取到 DDR 中，然后跳转到大 u-boot。</li>
</ul>
<p>如下图所示：</p>
<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/02IMX6ULL%E5%B9%B3%E5%8F%B0/LV05-uboot%E4%B8%8E%E5%86%85%E6%A0%B8/LV05-01-uboot-09-uboot%E4%B8%AD%E7%9A%84SPL/img/1.png" alt="img" style="zoom:50%;" />



<p>先假设，我们的代码，都已经放置到了外部存储器上，也就是绿色部分，然后会进行以下步骤：</p>
<ul>
<li>SoC厂家要做的事情：</li>
</ul>
<p>（1）上电后，BootROM 开始执行，初始化时钟，关闭看门狗，关 Cache，关中断等等，根据 Bootstrap Pin 来确定启动设备，初始化外设；</p>
<p>（2）使用外设驱动，从存储器读取 SPL；</p>
<ul>
<li>用户要做的事情：</li>
</ul>
<p>（3）SPL 被读到 SRAM 执行，此刻，控制权以及移交到我们的 SPL 了；</p>
<p>（4）SPL 初始化外部 DDR；</p>
<p>（5）SPL 使用驱动从外部存储器读取 u-boot 并放到 DDR；</p>
<p>（6）跳转到 DDR 中的 u-boot 执行；</p>
<p>（7）加载内核。</p>
<p>但是在实际情况中，还需注意很多问题：</p>
<p>（1）编译阶段的链接地址，是否需要地址无关？</p>
<p>（2）SPL 的代码和 u-boot 的代码是否有重合的地方？如果有，是否意味着 SPL 执行过的，跳转到 u-boot 又要在执行一次？</p>
<p>（3）具体情况下，需要配置哪些硬件？怎么配置？</p>
<h1 id="三、SPL框架？"><a href="#三、SPL框架？" class="headerlink" title="三、SPL框架？"></a><font size=3>三、SPL框架？</font></h1><p>其实在u-boot的文档中，给我们提供了一个通用的框架说明，我们打开u-boot源码目录中的doc&#x2F;README.SPL文件：</p>
<figure class="highlight txt"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br></pre></td><td class="code"><pre><span class="line">Generic SPL framework</span><br><span class="line">=====================</span><br><span class="line"></span><br><span class="line">Overview</span><br><span class="line">--------</span><br><span class="line"></span><br><span class="line">To unify all existing implementations for a secondary program loader (SPL)</span><br><span class="line">and to allow simply adding of new implementations this generic SPL framework</span><br><span class="line">has been created. With this framework almost all source files for a board</span><br><span class="line">can be reused. No code duplication or symlinking is necessary anymore.</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">How it works</span><br><span class="line">------------</span><br><span class="line"></span><br><span class="line">The object files for SPL are built separately and placed in the &quot;spl&quot; directory.</span><br><span class="line">The final binaries which are generated are u-boot-spl, u-boot-spl.bin and</span><br><span class="line">u-boot-spl.map.</span><br><span class="line"></span><br><span class="line">A config option named CONFIG_SPL_BUILD is enabled by Kconfig for SPL.</span><br><span class="line">Source files can therefore be compiled for SPL with different settings.</span><br><span class="line"></span><br><span class="line">For example:</span><br><span class="line"></span><br><span class="line">ifeq ($(CONFIG_SPL_BUILD),y)</span><br><span class="line">obj-y += board_spl.o</span><br><span class="line">else</span><br><span class="line">obj-y += board.o</span><br><span class="line">endif</span><br><span class="line"></span><br><span class="line">obj-$(CONFIG_SPL_BUILD) += foo.o</span><br><span class="line"></span><br><span class="line">#ifdef CONFIG_SPL_BUILD</span><br><span class="line">	foo();</span><br><span class="line">#endif</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">The building of SPL images can be enabled by CONFIG_SPL option in Kconfig.</span><br><span class="line"></span><br><span class="line">Because SPL images normally have a different text base, one has to be</span><br><span class="line">configured by defining CONFIG_SPL_TEXT_BASE. The linker script has to be</span><br><span class="line">defined with CONFIG_SPL_LDSCRIPT.</span><br><span class="line"></span><br><span class="line">To support generic U-Boot libraries and drivers in the SPL binary one can</span><br><span class="line">optionally define CONFIG_SPL_XXX_SUPPORT. Currently following options</span><br><span class="line">are supported:</span><br><span class="line"></span><br><span class="line">CONFIG_SPL_LIBCOMMON_SUPPORT (common/libcommon.o)</span><br><span class="line">CONFIG_SPL_LIBDISK_SUPPORT (disk/libdisk.o)</span><br><span class="line">CONFIG_SPL_I2C_SUPPORT (drivers/i2c/libi2c.o)</span><br><span class="line">CONFIG_SPL_GPIO_SUPPORT (drivers/gpio/libgpio.o)</span><br><span class="line">CONFIG_SPL_MMC_SUPPORT (drivers/mmc/libmmc.o)</span><br><span class="line">CONFIG_SPL_SERIAL_SUPPORT (drivers/serial/libserial.o)</span><br><span class="line">CONFIG_SPL_SPI_FLASH_SUPPORT (drivers/mtd/spi/libspi_flash.o)</span><br><span class="line">CONFIG_SPL_SPI_SUPPORT (drivers/spi/libspi.o)</span><br><span class="line">CONFIG_SPL_FAT_SUPPORT (fs/fat/libfat.o)</span><br><span class="line">CONFIG_SPL_EXT_SUPPORT</span><br><span class="line">CONFIG_SPL_LIBGENERIC_SUPPORT (lib/libgeneric.o)</span><br><span class="line">CONFIG_SPL_POWER_SUPPORT (drivers/power/libpower.o)</span><br><span class="line">CONFIG_SPL_NAND_SUPPORT (drivers/mtd/nand/libnand.o)</span><br><span class="line">CONFIG_SPL_DRIVERS_MISC_SUPPORT (drivers/misc)</span><br><span class="line">CONFIG_SPL_DMA_SUPPORT (drivers/dma/libdma.o)</span><br><span class="line">CONFIG_SPL_POST_MEM_SUPPORT (post/drivers/memory.o)</span><br><span class="line">CONFIG_SPL_NAND_LOAD (drivers/mtd/nand/nand_spl_load.o)</span><br><span class="line">CONFIG_SPL_SPI_LOAD (drivers/mtd/spi/spi_spl_load.o)</span><br><span class="line">CONFIG_SPL_RAM_DEVICE (common/spl/spl.c)</span><br><span class="line">CONFIG_SPL_WATCHDOG_SUPPORT (drivers/watchdog/libwatchdog.o)</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">Debugging</span><br><span class="line">---------</span><br><span class="line"></span><br><span class="line">When building SPL with DEBUG set you may also need to set CONFIG_PANIC_HANG</span><br><span class="line">as in most cases do_reset is not defined within SPL.</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">Estimating stack usage</span><br><span class="line">----------------------</span><br><span class="line"></span><br><span class="line">With gcc 4.6 (and later) and the use of GNU cflow it is possible to estimate</span><br><span class="line">stack usage at various points in run sequence of SPL.  The -fstack-usage option</span><br><span class="line">to gcc will produce &#x27;.su&#x27; files (such as arch/arm/cpu/armv7/syslib.su) that</span><br><span class="line">will give stack usage information and cflow can construct program flow.</span><br><span class="line"></span><br><span class="line">Must have gcc 4.6 or later, which supports -fstack-usage</span><br><span class="line"></span><br><span class="line">1) Build normally</span><br><span class="line">2) Perform the following shell command to generate a list of C files used in</span><br><span class="line">SPL:</span><br><span class="line">$ find spl -name &#x27;*.su&#x27; | sed -e &#x27;s:^spl/::&#x27; -e &#x27;s:[.]su$:.c:&#x27; &gt; used-spl.list</span><br><span class="line">3) Execute cflow:</span><br><span class="line">$ cflow --main=board_init_r `cat used-spl.list` 2&gt;&amp;1 | $PAGER</span><br><span class="line"></span><br><span class="line">cflow will spit out a number of warnings as it does not parse</span><br><span class="line">the config files and picks functions based on #ifdef.  Parsing the &#x27;.i&#x27;</span><br><span class="line">files instead introduces another set of headaches.  These warnings are</span><br><span class="line">not usually important to understanding the flow, however.</span><br><span class="line"></span><br></pre></td></tr></table></figure>


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    <p><span>文章标题:</span><a href="/post/c4232ca6.html">LV05-01-uboot-09-uboot中的SPL</a></p>
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